The Japanese Patent Publication No. 3367389 discloses calibration of overhead vehicles and stations in an overhead vehicle system. A large-scale system has at least 100 overhead vehicles and several hundred stations (stopped positions). When stoppage or transfer control data is calibrated for each combination of an overhead vehicle and a station, a heavy burden is imposed on the system. Accordingly, calibration is carried out using one of the overhead vehicles as a reference. Each of the other overhead vehicles stores a shift (deviation) from the reference overhead vehicle used for the calibration to correct calibration data.
When each overhead vehicle stores stoppage and transfer control data on several hundred stations, a considerably large storage capacity is required to store these data. Further, every time, for example, the arrangement of the stations is changed, the storage in a large number of overhead vehicles must be updated. It is thus cumbersome to change the arrangement of the stations or increase or delete stations.
In addition, as examples of a position sensor used for a machine tool, the Unexamined Japanese Patent Application Publication (Tokkai) No. 2001-174206, the Unexamined Japanese Patent Application Publication (Tokkai) No. 2003-139563 and the Unexamined Japanese Patent Application Publication (Tokkai) No. 2003-156364 disclose linear sensors using the magnetic coupling between coils and a magnetic mark composed of a magnetic or nonmagnetic substance or the like. When a plurality of detection coils are connected together in series and an alternating current is applied to the coils, the voltages of the detection coils change depending on the positional relationship between the magnetic mark and the coils. When the phase of each of the detection coils with respect to the magnetic mark is defined as θ and the angular speed of the alternating current flowing through the detection coils is defined as ω, a signal proportional to sin θ·sin ωt or cos θ·cos ωt is obtained on the basis of the change in voltage.